Problems to switch resolutions

["Ezequiel" <hreyes seg inf cu>]

I am using Linux RedHat 6.0 and the GNOME instalation that comes with it, I
have read that you can switch resolution by pressing CTRL-TAB and + or - on
the keypad, but it does'nt do anything. When y I first instaled RH Linux it
ran Xconfigurator and let me select resolutions from a list, I selected
1024x768 as default and also 800x600 with 16 bit color to make sure I could
work in high res and still be able to switch to 16 bit at any time to see
colorful pictures or drawings (I have 1 MB video RAM). But it does'nt work.
Any sugestion ?
Another question, I'm new to GNOME, is there a way to change the color sheme
of the windows (not the panels, but the rest of the interface) ?.
Thanks to all.